Pressure-sensitive adhesive tape from polypropylene



Feb. 26, 1963 H. A. NAUDAIN 3,079,278

PRESSURE-SENSITIVE ADHESIVE TAPE FROM POLYPROPYLENE Filed June 26, 1961 BACKING OF STEREOREGULAR POLYPROPYLENE HOWARD A. NAUDAI N INVENTOR.

AGENT Unite taes The present invention relates to a pressure-sensitive adhesive tape. More particularly, it relates to a pressuresensitive adhesive tape comprising a backing of stereoregular polypropylene film and an adhesive comprising a mixture of amorphous polypropylene and hydrogenated abietyl alcohol.

Typically, a pressure-sensitive adhesive tape comprises a flexible backing which may be, for example, paper, plastic film or cloth, having a normally tacky, pressuresensitive adhesive bonded thereto. A particularly well known and commonly used pressure-sensitive adhesive tape is one in which the flexible backing is cellophane. The pressure-sensitive cellophane tape on the market today has a three-fold balance of adhesion, cohesion, and viscoelasticity. Thus, although the tape is highly tacky, it can nevertheless be stripped from a smooth surface without delamination, splitting or transferring of the adhesive to the surface.

One of the newer plastics from which strong flexible film can be made is stereoregular, sometimes called isotactic, polypropylene. Film of this polymer is economically competitive with cellophane and has several advantages compared to cellophane, particularly improved water resistance and strength, and resistance to dimensional changes with changing humidity. On the basis of these qualities, film of stereoregular polypropylene offers obvious promise as a flexible backing for pressure sensitive adhesive tape.

The manufacture of satisfactory pressure-sensitive tape from stereoregular polypropylene fi-lm is, however, not a simple matter because the nature of stereoregular polypropylene is such that the known pressure-sensitive adhesives do not adhere readily to the polymer. Hence, when these conventional adhesives are applied to a backing of stereoregular polypropylene film, they are easily stripped from the film. Therefore, stereoregular polypropylene has been unable to compete with cellophane as a backing for a pressure-sensitive tape for lack of a satisfactory adhesive.

It is known from the art (see US. 2,927,047 to Schiilde et al.) that solid, amorphous polypropylene adheres quite strongly to a stereoregular polypropylene and, accordingly, the former polymer has been suggested as a primer for stereoregular polypropylene or as an ad hesive for bonding stereoregular polypropylene to itself.

Amorphous polypropylene is not, however, tacky at normal temperatures and, accordingly, it not per se useful as a pressure-sensitive adhesive.

In accordance with the present invention it has been found that amorphous polypropylene can be made permanently tacky -by admixture with hydrogenated abietyl alcohol and that the resultant mixture is an excellent pressure-sensitive adhesive for use on a backing of stereoregular polypropylene film. Accordingly, the invention is directed to a pressure-sensitive adhesive tape which, as

ice

shown in the attached cross-sectional drawing, comprises a backing of stereoregular polypropylene 'film and an adhesive layer comprising a mixture of hydrogenated abietyl alcohol and solid amorphous polypropylene.

The adhesive composition employed in the invention is critical from the standpoint of both the adhesive, i.e., amorphous polypropylene and the tackifying ingredient, i.e., hydrogenated abietyl alcohol. Thus, for instance, satisfactory pressure-sensitive adhesives for stereoregular polypropylene film do not result when amorphous polypropylene is replaced with other adhesives disclosed for use in pressure-sensitive compositions, such as natural rubber, polychloroprene, and polyisobutylene. Similarly, the replacement of hydrogenated abietyl alcohol with materials that have been recommended as tackifiers in pressure-sensitive adhesive compositions leads to unsatisfactory results. These results indicate on one hand the diffioulty of providing an adhesive that will adhere satisfactorily to stereoregular polypropylene and, on the other hand, the inability of amorphous polypropylene to respond generally to tackifying agents.

The following examples are presented in further illustration of the invention. Parts and percentages are by weight unless otherwise specified.

EXAMPLE 1 An adhesive solution was prepared by adding two parts of hydrogenated abietyl alcohol (a commercial mixture of tetrahydroabietyl alcohol and dihydroabietyl alcohol) to 10 parts of a 10% solution of amorphous polypropylene in n-heptane.

The amorphous polypropylene employed in this and all subsequent examples had a reduced specific viscosity of 2.8 determined on a 0.1% solution of the polymer in decahydronaphthalene at 135 C. and a molecular weight of about 430,000.

The adhesive solution was cast onto an unoriented 5- mil film of stereoregular polypropylene to give an as cast thickness of 25 mils. The coated film was then air dried at to C. for 10 minutes which resulted in a dried adhesive layer thickness of 3.0 mils. A piece of the coated film measuring 1 inch by 3 inches was then applied by finger pressure to a 1.5 mil uniaxially oriented film of stereoregular polypropylene. The peel strength of the pressure-sensitive film was then determined on a Scott model LACC tester at the rate of 12 inches per minute, using a T-peel and allowing the stiffness of the two plastics, i.e., the backing and the substrate, to determine the exact angle of peel. The peel strength was found to be 5.0 pounds per inch of width. During the peeling the adhesive layer adhered firmly to its backing with no delamination or splitting of the adhesive layer. Also, samples of the tape were stored for weeks without loss of tackiness.

EXAMPLES 2 TO 11 v in which the weight ratio of hydrogenated abietyl alcohol to amorphous polypropylene was varied over a wide range. The results are tabulated below:

her) and the tapes tested for peel strength as described in Example 1. The results were as follows:

disappearedafter a short period of storage.

In another series of experiments pressure-sensitive tapes wereprepared as .describedin Example 1 but substituting various polymers for amorphous polypropylene (while retaining hydrogenated abietyl alcohol as a tacki- Table I Table III Ratio, Natural Polyiso- Polyehloro- Hydrogenated Thickness Peel Rubber butylene prone abletyl 01 Dry Strength EX. No. Alcohol] Backing Adhesive (lb./inv

orp ous (mils) width) PercentSolidsinBaseSolu- 9 l2.

Polyprotion.

Py fi e Solvent n-heptano nheptane toluene.

10 Ratio, Hydrogenated 3:2 3:2 3:2. I Abietyl Alcohol/Rubber. 2/1 Uniaxially oriented 2.7 3.1 Total Percent Solids in Ad- 21.8 19.8 r. 25.4.

polypropylene hesive Solution. film. Wet Cast Thinkne 1s 15. 1.0 2.2 Average PeelStrength 0.8 1.9 0.8. 4 2.0. 2.1 Quality of Adhesive Bond Very Poor Very Poor Poor (50% I ..d0 1.5 2.0 15 to Backing. 100 a 00% trausicr). 2 1 Unoriented poly- 2.5 4.3 transfer). transfer).

propylene film .2/1 d 1.5 3.7

It can be seen from the data in the preceding table 1.4 2.7 g2 that the other polymers examined do not provide adhesives that adhere satisfactorily to the stereoregular polypropylene backing because in each case there was transfer of adhesive to the substrate when the tape was There was no delamination or splitting of the adhesive peeled from the substrate. layer in any vof the foregoing experiments. The data The examples have demonstrated the unique qualities .show that the ratio oftackifier to amorphous polypro- Of an adhesive tape comprising a backing of stereo- ,pylene is desirably from about 1.5:1 to 2:1'for optimum regular polypropylenefilrn and an adhesive layer comstrength. Howeverg-ratios as low as 0.5 to 1 give a satisprising a mixture of solid amorphous polypropylene and factory tape. hydrogenated abietyl alcohol.

The term hydrogenated aibietyl alcohol isernployed EXAMPLE 12 in the specification in generic sense to include the alco- I'I'he: ressu re sensitive adhesive ta es of Exam les 6 hols.denved from the l-iydmgenanon of ab1.ty1 alcqhol jand :7 g applied by rfingerlpressulze to variouspother specifically tetrahydroabietyl alcohol and dihydroabietyl substrates including glass, cellophane, and poly(ethylene i g gi' g gggii zg g zg g ggggi g fig gig tere hthalate Th z e peel stmngth results are tabulated either of the hydrogenated alcohols may be used alone in the practice of the invention to give results e uiva- Table 11 lent to the commercial mixture. In preparing the adhesive composition that is employed aii-gig? in the invention the hydrogenated abietyl alcohol and Substrate 40 amorphous polypropylene are simply admixed in the de- Tape of Tape of sired ratio. The prefered procedure to mix the two in- Examplefi Example 7 gredients in solution in a suitable solvent such as paraffinic hydrocarbon in the ratio of hydrogenated abietyl Glas 5.4 4.3 alcohol to amorphous polypropylene may reasonably i fii htt feitsrsnraaa'as:::: i: i1 i1? vary from about 0-5110 about by Weight- The solid amorphous polypropylene employed as the In. all cases there was no transfer of adhesive from the other component of the .adheswe P may vary tape backing to the Substrate Widely in molecular weight but desirably will have a molecular weight of from about 120,000 to about I 1,000,000. COMPARATWE EXAMPLES The pressure-sensitive adhesive tape of the invention In other experiments the criticality of the adhesive is s y p p y rch/ s a layer of the adheswe characteristics of the invention toboth of the compo Solution to one Of both surfmfes of a ital'eoregulal' nents has been demonstrated by attempting various sub- P YP PY and evaporating the Sohd from the stitutions. In one series of experiments various comadhesive y heafimg to elevated QP f mercial materials that have been recommend as tackifyamount of adheslve pp to the backlng film 15 ing ingredients for other polymers were evaluated as ablfi Over a Wldfl l P Y, l Should tackifiers for amorphous polypropylene. The adhesives be $1011 35 t0 P after y l an l resulting from the substitutions were applied to unorihavlfig a thickness of mil to about 5 H1113- ented of stereo -egular polypropylene and I claim and desire to PTDteCt Letters Patent resultant pressure-sensitive tapes were examined quali- 151 tatively for degree of tack. It was found that none of lil'essllf-e-sefl51Hve adhfislve p compflslflg a the potential tackifiers so examined were comparable backmg 0f stel'eoreglllfil' P YP 9PY film and an :to hydrogenated abietyl alcohol in providing pressurehelve layer comprlsms a mlXtule 0f y sensitive properties to the amorphous polypropylene. f y 31001191 5011(1 amorphous p lyp py In The materials tested were hydrogenated rosin, chlorinated 35 WhICh the Welght Iatlo 0f hydfogqlated ablety} alcohol to paraflin, the glycerol ester of hydrogenated rosin, polym- Solid amorphous p lyp gy e from 0-311 t0 erized sulfate turpentine, m-pinene dimer, terpene resins, The p of Clalm 1 111 Yvhlcflihe amOIPhOUS p l'- and hydrocarbon resins. Of these, only chlorinated P py has a molecular Welght 0f from about 120,000 paraffin imparted more than-a very slight surface tack to to the amorphous polypropylene, but the surface tack References Cited in the fil of this patent UNITED STATES PATENTS 2,825,721 Hogan et al Mar. 4,.1958 2,927,047 Schulde et a1. Mar. 1, 1960 2,947,650 Gerhardt et all Aug. 2, 1960 

1. A PRESSURE-SENSITIVE ADHESIVE TAPE COMPRISING A BACKING OF STEREOREGULAR POLYPROPYLENE FILM AND AN ADHESIVE LAYER COMPRISING A MIXTURE OF HYDROGENATED ABIETYL ALCOHOL AND SOLID AMORPHOUS POYLPROPYLENE IN WHICH THE WEIGHT RATIO OF HYDROGENATED ABIETYL ALCOHOL TO SOLID AMORPHOUS POYLPROPYLENE IS FROM 0.5:1 TO 3:1. 